Models of contractility and stiffening of the cell cytoskeleton

Understanding the effect of motor proteins, such as myosins, on the elasticity of cross-linked actin networks is essential to our understanding of cell mechanics. Both in vivo and in vitro, these active networks have radically different mechanical properties from their equilibrium counterparts, including contractile behavior and higher elastic moduli[1,2].

One dimensional active bundle simulation, with oriented filaments (dark red, dark green), passive crosslinks (black) and active crosslinks (red).

Inspired by the recent experiments of the Gardel group [3], we are currently working on a one dimensional lattice model with minimal ingredients, that is, rigid polar filaments, spring-like passive crosslinks and active crosslinks with on/off dynamics implemented through non-equilibrium Monte Carlo solution of the corresponding master equations. We find that the network needs to be percolated through the passive crosslinks to be mechanically stable and macroscopically contractile. Contractile behavior is observed for all concentrations of active crosslinks, and we present a novel mechanism based on the asymmetric on/off dynamics of the links.

[1] G. H. Koenderink, Z. Dogic, F. Nakamura, P. M. Bendix, F. C. MacKintosh, J. H. Hartwige, T. P. Stossele, and D. A. Weitz, PNAS 106, 15192 (2009).

[2] S. Köhler, V. Schaller and A. Bausch, Nature Materials 10, 462 (2011).

[3] T. Thoresen, M. Lenz, and M. L. Gardel, Biophys. J., 100(11):2698–2705, 2011.